Interlock mechanisms for controlling the operation of the shift lever of an automobile transmission are known. In general, these mechanisms are utilized to prevent movement of the shift lever from a given position until certain prescribed conditions are met. For example, it is usually desirable for the interlock mechanism to prevent shifting an automatic transmission from the park position when the engine is running unless the driver has applied the brakes.
One prior interlock utilizes a solenoid for controlling a latch, which engages a movable part of the shift mechanism in the form of a bar. The latch captures the bar when in the locked position and releases the bar when in the unlocked position. The logic of this arrangement is that the solenoid holds the latch in the locked position when the solenoid is energized and allows the latch to be moved from the locked position when the solenoid is not energized. Thus, in that system, the transmission is prevented from shifting from the park position only when the ignition is on and the solenoid energized.
Other known interlock mechanisms use a solenoid to hold a lock member in the locked position when the solenoid is energized.
These prior interlock mechanisms are mechanically complicated and require the solenoid to be energized to activate the interlock. This means that the interlock only works when the ignition is on and that the solenoid is always energized when the ignition is on and the brakes not applied. Constant energization of the solenoid places additional physical demands on the solenoid itself and requires a continuous supply of electric current. The requirement for a continuous supply of current is a particular disadvantage in electric cars. It is possible to employ an electronic circuit that senses when the transmission has been shifted out of the park position to deactivate the solenoid, but these systems are more complicated and require an additional element to sense when the transmission is not in "park". These park sensing system have also been used to eliminate the clicking sound of the solenoid heard by the driver as the brakes are activated or released.
Interlocks are also known that operate when the ignition is off. These systems, however, have required separate mechanical elements such as a slide mechanism.